Continuous thickness measuring apparatus for veneer and other web material

ABSTRACT

In apparatus including a pair of relatively movable feeler wheels for continuously measuring the thickness of a traveling web, the stationary part of the transducer which detects the movements of the movable wheel is mounted on a supplemental frame fixed with relation to the support for the stationary wheel and capable of sufficient movement with respect to the structure supporting the movable wheel to be independent of shock and vibration forces affecting that structure.

United States Patent Plough 51 Aug. 1, 1972 [54] CONTINUOUS THICKNESSMEASURING APPARATUS FOR VENEER AND OTHER WEB MATERIAL [72] Inventor:Irving L. Plough, Everett, Wash.

[73] Assignee: The Black Clawson Company,

Hamilton, Ohio [22] Filed: Oct. 30, 1970 [21] Appl. No.: 85,418

[52] U.S. Cl ..33/143 L, 33/147 L, 33/147 N [51] Int. Cl. ..G01b 5/02,GOlb 5/04, GOlb 5/06 [58] Field of Search..33/l43 F, 143 L, 143 R, 147R,

[56] References Cited UNITED STATES PATENTS 3,140,545 7/1964 Murtland..33/143 L 2,955,358 10/1960 Walking ..33/143F Primary Examiner-LeonardForman Assistant Examiner-Paul G. Foldes Attorney-Marechal, Biebel,French and Bugg 57] ABSTRACT ln apparatus including a pair of relativelymovable feeler wheels for continuously measuring the thickness of atraveling web, the stationary part of the transducer which detects themovements of the movable wheel is mounted on a supplemental frame fixedwith relation to the support for the stationary wheel and capable ofsufficient movement with respect to the structure supporting the movablewheel to be independent of shock and vibration forces affecting thatstruc- 7 Claims, 5 Drawing Figures PATENTEDAus 1 I972 SHEET 1 0F 2 Illliw mm F INVENTOI? IRVING L. PLOUGH IOT I55 ISI A TTORNEYS CONTINUOUSTHICKNESS MEASURING APPARATUS FOR VENEER AND OTHER WEB MATERIALBACKGROUND OF THE INVENTION Wood veneers of the types most used in themanufacture of plywood are produced on a lathe wherein a log or bolt ofwood is rotated about its longitudinal axis with respect to a knifewhich peels the wood to form a continuous web. Commonly a nose barengages the wood at a position close to the edge of the knife, and thethickness of the veneer is primarily determined by the spacing of theknife edge with respect to this nose bar. The web is carried from thelathe on a conveyor system which includes a table where a clipper of theguillotine type cuts the web into sections of predetermined width in thedirection of travel, and also cuts out sections containing holes orother defects rendering them unfit for plywood use.

It is important to a veneer producer to maintain the thickness of theveneer as nearly as possible uniform within predetermined tolerances,for a number of reasons. One such reason is that when several layers ofveneer, sometimes of different thicknesses and types, are combined inplywood, any significant variation in the thickness of one or anotherlayer could cause unacceptable thickness variations in the plywood.Further, it is customary in the industry to grade veneer for sale inaccordance with a guaranteed minimum thickness, e.g., 543 inch veneer isall at least one-eighth inch in thickness but may vary above thatthickness. Since the veneer producer is paid only on the basis of therated minimum thickness, any excess thickness represents a loss to himof potential additional income.

A related factor is that the smoothness of veneer directly affects itssales value, and this is a property which is in large measure determinedby the sharpness of the lathe knife. As the knife edge wears in use, thethickness of the veneer will tend to increase unless the knife isreadjusted to bring its edge closer to the nose bar, and also rougheningof the veneer surface will tend to increase, both of which areeconomically undesirable conditions. Since, therefore, the operatingcondition of the knife is reflected in the thickness and surfacecondition of the veneer, continuing accurate measurement of the veneerthickness would serve as a constant source of information as to the needfor readjustment, sharpening or replacement of the knife.

The usual practice has been to caliper the sheet at fairly frequentintervals, but there is obviously a lag between the time wheninformation is obtained in this manner and the time when action could betaken on the basis of that information. Further, calipering requiresthat the veneer be stationary, which means that the measurement must bemade on a piece pulled away from the conveyor. Continuous measuringapparatus, however, must compete with a variety of operatingdifficulties, including the presence of pitch or gum on the surface ofmany woods, and also the excessive shock and vibration forces incidentto the normal operating conditions of a veneer mill, and particularlycontributed to by the frequent and rapid blows of the clipper blade onits complementary anvil.

SUMMARY OF THE INVENTION It is the primary objective of this inventionto provide apparatus which will continuously and accurately measure thethickness of a veneer web by continuously monitoring the web as ittravels from the lathe to the clipper, and which will supply acontinuous record of the thickness information in a convenient form foruse. To accomplish this objective, the invention successfully overcomesthe major difficulties noted above, and including particularly thepresence of pitch and other substances on the surface of the veneer, andthe shock and vibration forces generated by the clipper and otherapparatus customarily present in a veneer mill.

The apparatus of the invention includes a pair of feeler members such asmeasuring wheels arranged for movement toward and away from each otherwhile respectively engaging the bottom and top surfaces of the advancingveneer web. The bottom wheel is provided with a relatively firmmounting, the upper wheel is biased downwardly into engagement with thesurface of the veneer web riding on the lower wheel, and the thicknessof the web is monitored by continuously measuring the movements of theupper wheel toward and away from the lower wheel. The effects of foreignsubstances on the surface of the veneer are minimized by arranging thewheels at a small angle to each other and the direction of web travel,such that they are essentially self cleaning.

As already noted, a major problem affecting any such measuring apparatusis that its accuracy depends upon the extent to which the movements ofthe movable measuring member are due solely to variations in thethickness of the material being measured, as distinguished frommovements caused by the environmental forces such as shock and vibrationwhich are particularly prevalent in a veneer mill. At the same time,however, since a veneer web is normally somewhat more than eight feet inwidth, the mountings of measuring wheels on opposite sides of the webare necessarily spaced a substantial distance from each other.Notwithstanding this difficulty, the invention successfully minimizesshock and vibrational elfects by a construction and arrangement suchthat the stationary member of the transducer which senses movements ofthe upper measuring wheel is effectively rigidly interconnected with themounting for the lower measuring wheel so that movements of the upperframe due to shock or vibration do not affect the accuracy of thecontinuous measurement of web thickness.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective viewillustrating an installation of the measuring device of the inventionfor continuously measuring the thickness of a traveling web of veneernear one edge thereof;

FIG. 2 is an enlarged fragmentary side view, partly in section, of theinstallation of FIG. 1;

FIGS. 3 and 4 are enlarged fragmentary sections on the lines 3-3 and 44respectively of FIG. 1; and

FIG. 5 is a somewhat diagrammatic elevation showing another form ofinstallation of the invention for continuously measuring thickness at aplurality of spaced positions across the width of a traveling web.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The installation of theinvention illustrated in FIG. 1 is arranged for continuous monitoring ofthe thickness of a web W of veneer carried by multiple conveyor belts10. Preferably the measuring will be done at a location between theveneer lathe and the clipper, in order to provide a continuous measuringoperation uninterrupted by the separation of adjacent pieces. Themeasuring is accomplished by continuous monitoring of the relativedisplacement of a pair of wheels 11 and 12 which respectively engage thelower and upper surfaces of the web. The supporting structure for wheels11-12 is designed to limit measurement of the relative movements ofthese wheels to the travel caused by variations in the thickness of theveneer, as distinguished from shock, vibration and other forces incidentto operation of the mill.

The main frame in FIG. 1 comprises an end stand 13 from which lower andupper frame arms 14 and 15 are cantilevered in vertically spacedrelation to define an open ended slot 17 for receiving the veneer web Wtherethrough. The stand 13 is mounted on base means, such as angles18,-in predetermined relation to the path of the veneer so that the arms14 and 15 extend above and below the veneer at a location such that thelower measuring wheel engages a portion of the veneer between conveyorbelts 10 at a location spaced inwardly from the adjacent edge of theweb, for example about 36 inches.

The lower measuring wheel 11 is provided with a fixed mounting on top ofthe inner end of the lower frame arm 14. This mounting comprises a fork20 which carries the axle 21 for wheel 11 and is in turn bolted on topof a mounting pad 22 forming in effect a part of the frame arm 14.

The upper measuring wheel 12 is supported in the upper frame arm 15 insuch manner that it is free to move vertically as required by variationsin thickness of the veneer, independently of any movements of the frameresulting from shock or vibrational forces. Referring particularly toFIG. 2, the wheel 12 is mounted by an axle 24 in a fork 25 which is inturn bolted to the head 26 of an elongated cylinder 30. The barrelportion of the cylinder 30 is in turn supported by bearings 33 and aspacer 34 for free movement in a housing 35 bolted or otherwise mountedon the end wall 36 of the frame arm 15. It has been found desirable inthe practice of the invention to use ball bushings as the bearings 33,protected by a suitable seal 37 at the lower end of the housing 35.

A piston rod 40 includes an enlarged head 41 bolted or otherwisesecuredv in stationary relation with the upper end of the housing 35.The cylinder 30 is accordingly movable axially with respect to thepiston rod 40, and its movements are guided along a substantiallystraight vertical path by a roller follower 42 supported in a fork 43mounted on a bracket 44 secured to or forming a part of the cylinderhead 26. The roller 42 rides in a slot 45 in the end wall 36 and thusmaintains the wheels 1 1-12 in the desired arrangement shown in FIGS.1-2 wherein their central planes are aligned at small angles to eachother and to the direction of travel of web W to provide a continuousself-cleaning action with respect to pitch, gum or the like on thesurface of the veneer.

The piston rod 40 has a threaded lower end portion on which a piston 46is mounted by a nut 47, and the 5 piston 46 carries an O-ring 48 insealing engagement with the inner surface of the cylinder 30. The piston46 and O-ring 48 thus divide the interior of the cylinder 30 into lowerand upper portions 50 and 51 which are provided with pressure andventing connections for selectively biasing the cylinder 30 in thedesired direction. A passageway 52 leads from a port 53 in the pistonrod head 41 through the lower end of the piston rod into the chamber 50,and a second passage 55 leads from a port 56in the side of the pistonrod 40 above the piston 46 to a port 57 in the upper end of the pistonrod. In normal operation, the port 53 is connected to a source ofpressure air to supply pressure to the chamber 50 while the port 57 isconnected to atmosphere. Preferably, however, the pressure system willinclude provisions for reversing these connections to supply pressure tothe chamber 51 while chamber 50 is connected to atmosphere, as indicatedby the pressure control valve 58.

With this construction and control system as thus far described, thecylinder 35 will in normal operation be pressure loaded downwardly sothat the upper measuring wheel 12 will be biased into engagement withthe upper surface of a veneer sheet traveling between wheels 11-12. Anyvariations in the thickness of the veneer will produce corresponding upor down movement of the wheel 12 and cylinder 30, and these movementsare constantly monitored by a transducer mechanism 60 as describedbelow. It should be noted first, however, that when the pressure supplyconnections are reversed, the cylinder 30 will rise and thereby separatethe measuring wheels 11-12 to the extent of the upward'travel of thecylinder 30, thereby providing corresponding clearance between the twowheels for maintenance purposes and the like.

It is essential to the success of the invention that the mechanism 60for measuring movement of the upper wheel 12 toward and away from wheel1 1 respond only to movement of wheel 12 caused by variations in thethickness of the veneer passing therebetween, and that it be able toignore all forces causing movement of upper frame arm 15 with respect toother parts of the frame, a particular problem being the tendency of thearms 14 and 15 to move toward and away from each other with a tuningfork effect. The transducer 60 is accordingly supported by asupplemental frame in the form of a generally C-shaped yoke 65positioned within the frame parts 13-15 and mounted on the lower framearm 14 in close proximity to the lower measuring wheel 11. As best seenin FIGS. 1 and 3, the lower end of the yoke 65 is forked to provide apair of short arms 66 which straddle the mounting pad 22 and aresupported for limited pivotal movement with respect to the frame arm 14on a pivot axis extending in the direction of travel of the veneer weband essentially coinciding with the vertical center line of the wheel10.

The pivotal mounting for one of the fork arms 66 is shown in detail inFIG. 3. It includes a pivot block 70 having is upper surface tapered toform a knife bearing 71 on which the lower surface of the fork arm 66rests. The fork arm 66 is provided with a tapered bore 72 which receivesa complementary tapered rubber grommet or washer 73 enclosing a metalsleeve 84, and a bolt 75 extends through this sleeve and is threadedinto a tapped bore in the upper wall of the frame arm 14. With thisconstruction, which is duplicated for the other fork arm 66, the yoke isheld firmly against the blocks and thereby substantially located in thehorizontal plane, but at the same time, it can have limited pivotingmovement on the blocks 70 to the extent permitted by distortion of thegrommet 73, which will normally be no more than a minor fraction of adegree.

The yoke 65 is designed to possess a high degree of rigidity such thatits two end portions will at all times remain in essentially fi-xedspaced relation, and the series of spaced holes 77 are provided todecrease its overall weight without detracting from the desiredrigidity. Its upper portion is therefore guided in the end stand 13 andupper frame arm 15 but is not rigidly connected to either of those frameparts. A pair of links 80 are pivoted at 81 to the upper arm of the yoke65 and at 82 to the frame arm 15 to permit this part of the yoke to moveas required to accommodate vertical movement of the arm 15 with respectto the bearing blocks 70.

An additional flexible support 85 is provided for the mid-portion of theyoke 65 in the end stand 13 and is shown in detail in FIG. 4. One end ofa rod 88 is supported for limited movement on the wall of end stand 13by a flat bar 90 secured to the wall by screws 91 and clamped between apair of rubber bushings 92 and nuts 93 on the rod 88. The other end ofthe rod 88 extends through a hole in the yoke 65 and is similarlyclamped to the yoke by a second pair of rubber bushings 92 and nuts 93.This supporting arrangement stabilizes the yoke in position within theend stand 13 while still providing for such limited movement as may berequired to compensate for vibration and shock effects on the frame.

The transducer mechanism 60, which is mounted in a bracket portion 99 onthe outer end of the upper arm of the yoke 65 may be selected from anumber of commercially available units capable of converting movement ofits movable part into electrical signals proportional to the extent ofthe movement. The transducer 60 is shown somewhat diagrammatically inFIG. 3 as a linear differential transducer Model 7DC DT-25O manufacturedby the Sanborn Division of Hewlett- Packard Company, and comprising astationary coil assembly 100 and a central probe 101 attached to thecore (not shown) which is movable axially within the coil assembly 100.Movement of the probe 101 is guided by the inner wall of the annularhousing 102, and a coil spring 105 normally biases the probe 101upwardly with respect to the coil assembly. The electrical leads 106 tothe coil assembly 100 are brought out through the wall of the housing102 and through an annular spacer 107 positioned between the coilassembly 100 and the spring 105.

The transducer housing 102 is in turn provided with an adjustable butfirm mounting in the end of the upper arm of the yoke 65. An annularmounting plate 110 is screwed or otherwise secured to the lower end ofthe housing 102, and this plate includes a tubular stem 111 mounted foraxial movement in a bore in the annular bracket portion 99 at the end ofthe yoke 65. The mounting plate 110 is provided with a key 112preventing it from rotating in the bracket 99, and a coil spring 113 ispositioned between the upper surface of the bracket 99 and the underside of the mounting plate 110. An adjusting knob 115 engages the underside of the bracket portion 99, and its screw portion is threaded intothe tapped interior of the stem 11]. The spring 113 biases the mountingplate 110 upwardly from the bracket portion 99, and rotation of the knob1 15 in one direction or the other will cause corresponding movement ofthe housing 102 with respect to the bracket 111 for accurate positioningand calibration of the transducer.

The movements of the upper measuring wheel 12 are transmitted to theprobe 101 by a wand of generally Z-shape which is screwed or otherwisemounted on the bracket portion 44 of the cylinder head 26. The upper endof the wand 120 overhangs and engages the upper end of the probe 101,and the adjusting knob 115 is used to adjust the relationships of theparts to a desired reference position of wand 120 and probe 101. Thisentire mechanism is shielded within the frame arm 15 except for theportion depending below the frame arm, which is enclosed within a shielddepending from the frame arm 15 and open at its lower end for access tothe adjusting knob 115.

In operation, the adjusting knob 115 is used to establish the desiredreference position of the probe 101 and wand 120 corresponding to apredetermined relative spacing of the wheels 11-12. For example, thisreference position may correspond to the guaranteed minimum thickness ofthe veneer to be monitored or to a selected intermediate position in thetolerance range above such minimum thickness. Then with the system inoperation and the veneer web traveling between the measuring wheels,whatever vertical movements occur on the part of the upper wheel 12 willbe sensed by the probe 101 and translated into electrical signals inaccordance with the characteristics of the transducer 60.

The physical and mechanical arrangements of the parts are such that thevertical movements of the wheel 12 will be effectively independent ofrelative movements of different parts of the frame structure, and willtherefore truly represent various thicknesses in the web W. This resultis achieved because the coil 100 and housing 102 are held in effectivelyrigid relation, through the yoke 65, with the lower measuring wheel 11and do not follow movements of the upper frame arm 15 such as may becaused by shock, vibration and other environmental and operationalconditions. Further, the upper measuring wheel is also independent ofsuch frame movements, because it is continually pressure biased againstthe upper surface of the veneer web, and while movements of the framearm 15 could cause the housing 35 to move up and down, the cylinder 30will remain in fixed relation with the upper surface of the veneer web.The flexible supports for the yoke 65 provided through the links 80 androd 88 also contribute to the desired result of maintaining the yoke 65and the parts supported thereby in rigid relation with the lower framearm 14 and isolated from relative movements of the end frame 13 andupper frame arm 15.

The electrical inputs to the transducer 60 are dictated by theelectrical characteristics of the transducer, as recommended by itsmanufacturer. The output 130 of the transducer may take a variety offorms and used for different selected purposes. For example, it may takethe form of a digital read out or a tape or other permanent read outrecord. Alternatively, as indicated at 131, it may be employed tocontrol mechanical means for implementing the monitoring function, suchfor example as an adjusting mechanism for the nose bar of the veneerlathe, a device for marking the veneer to indicate thick and thin areas,or the actuating control for the clipper to cause it to separate lengthsof veneer web in accordance with their variations from the desiredthickness.

FIG. illustrates the application of the invention to an installation formonitoring the thickness of a traveling veneer web at a plurality oflocations spaced across its width, and particularly useful where thewidth of the web is such that the cantilevered construction of FIGS. l-4may not be practical. In FIG. 5, the main frame comprises a base 150 anda pair of end stands 151 connected at their upper ends by a top frame152 which is spaced above the base 150 to define the opening 153 throughwhich the web travels on conveyor tapes 10. The installation shown inFIG. 5 includes three pairs of measuring wheels 155-156, each of thesepairs being individually essentially the same as the wheels 11-12 andcooperating in similar fashion to provide continuous measuring of thethickness of the web traveling therebetween.

In accordance with the invention, each of the pairs of measuring wheels155-156 and their associated apparatus are supported in essentially thesame relation with the base 150 as the wheels 11-12 and their associatedapparatus already described. More specifically, each lower wheel 155 hasa pivotal support fixed on the base 150, and each of the upper wheels156 is supported on the top frame 152 for vertical movement with respectto its complementary lower wheel. Thus the mounting 158 for each upperwheel 156 may be of essentially the same construction as the mountingfor wheel 12 described in connection with FIG. 3.

The transducer 160 for each pair of wheels 155-156 includes a stationarypart mounted in essentially stationary relation with the base 150 by asupplemental frame 165 which corresponds in function to the yoke 65 butis a complete annulus proportioned for enclosure within the fourcomponents. of the frame in similarly enclosing relation with theopening 153. As in the case of the yoke 65, the supplemental frame 165is preferably as light in weight as is compatible with high rigidityunder the operating conditions of the invention, and it is similarlyprovided with multiple holes for reducing its overall weight.

The supplemental frame 165 is mounted in the base 150 at locations closeto one or more of the lower measuring wheels, and two such mountings 166are shown as desirable in view of the overall dimensions of theinstallation. Each of the mountings 166 should secure the frame 165 inmetal-to-metal supported relation with the base 150 to retain the lowermeasuring wheel 155 in vertically fixed position with respect to thebase 150. For example, the mounting 166 could include a knife edgesupport of the same operating characteristics as the mounting for theyoke 65 as shown in FIGS. 2 and 3. In order to allow for relativemovement of the upper portion of the frame 165 and the top frame 152,the upper part of the supplemental frame 165 may be provided withstabilizing supports like the assembly shown in FIG. 4, and two suchsupports are indicated diagrammatically at 170.

The upper portion of the supplemental frame which lies within the frametop 152 and in the upper portion of the opening 153 corresponds infunction to the end of the upper arm portion of the yoke 65, and thestationary portion of the transducer associated with each of the uppermeasuring wheels is mounted thereon, by means which may be essentiallythe same as described in connection with FIG. 3. Accordingly, since thesupplemental frame 165 is essentially independent of movements of theend frames 151 and top frame 152 with respect to the base 150, itsupports the transducers in'essentially stationary position offering thesame advantages as described in connection with FIGS. l-4.

While the forms of apparatus herein described constitute preferredembodiments of the invention, it is to be understood that the inventionis not limited to these precise forms of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. Apparatus for continually measuring the thickness of a moving webcomprising:

a. a main frame including a base and a top connected in verticallyspaced relation to define an opening for receiving the web therethrough,

b. a lower wheel having a fixed mounting on said base and engageable bythe under surface of the web,

c. an upper wheel engageable by the top surface of the web,

(1. means on said frame top supporting said upper wheel for movementtoward and away from said lower wheel in accordance with variations inthe thickness of the web traveling therebetween,

e. a supplemental frame of rigid construction including upper and lowerportions connected in spaced relation defining an opening coincidingwith at least a portion of said opening in said main frame,

f. means mounting said lower frame portion in fixed relation with saidbase at a location adjacent said lower wheel,

g. transducer means including a pair of relatively movable members formeasuring movement of said upper wheel toward and away from said lowerwheel,

. means securing one of said transducer members to said upper portion ofsaid supplemental frame, and

i. means connecting the other of said transducer members to saidsupporting means for said upper wheel for movement therewith withrespect to said frame top.

2. The apparatus defined in claim 1 wherein said means connecting saidlower frame portion to said base comprises resilient means providing forlimited movement of said supplemental frame about a horizontal axissubstantially aligned with the vertical center lines of said wheels.

frame with respect to said main frame within the limits 1 established bysaid resilient means to isolate said supplemental frame from the effectsof relative movement of said base and top.

5. The apparatus defined in claim 1 wherein said upper and lowerportions of said supplemental frame are interconnected by a mid-portiondefining therewith a substantially C-shaped yoke with said upper andlower portions extending substantially normal to the direction ofmovement of said upper wheel on said frame top.

6. The apparatus defined in claim 5 wherein said mounting means (f)comprises 1. pivot means mounted on said frame base in sup portingengagement with said lower frame portion, and

2. resilient spacer means connected between said lower frame portion andsaid pivot means to limit relative movement of said supplemental frameabout said pivot means.

7. The apparatus defined in claim I wherein said upper and lowerportions of said supplemental frame are interconnected at both endsthereof by end portions cooperating therewith to enclose said openingfor receiving the web therethrough.

1. Apparatus for continually measuring the thickness of a moving webcomprising: a. a main frame including a base and a top connected invertically spaced relation to define an opening for receiving the webtherethrough, b. a lower wheel having a fixed mounting on said base andengageable by the under surface of the web, c. an upper wheel engageableby the top surface of the web, d. means on said frame top supportingsaid upper wheel for movement toward and away from said lower wheel inaccordance with variations in the thickness of the web travelingtherebetween, e. a supplemental frame of rigid construction includingupper and lower portions connected in spaced relation defining anopening coinciding with at least a portion of said opening in said mainframe, f. means mounting said lower frame portion in fixed relation withsaid base at a location adjacent said lower wheel, g. transducer meansincluding a pair of relatively movable members for measuring movement ofsaid upper wheel toward and away from said lower wheel, h. meanssecuring one of said transducer members to said upper portion of saidsupplemental frame, and i. means connecting the other of said transducermembers to said supporting means for said upper wheel for movementtherewith with respect to said frame top.
 2. The apparatus defined inclaim 1 wherein said means connecting said lower frame portion to saidbase comprises resilient means providing for limited movement of saidsupplemental frame about a horizontal axis substantially aligned withthe vertical center lines of said wheels.
 2. resilient spacer meansconnected between said lower frame portion and said pivot means to limitrelative movement of said supplemental frame about said pivot means. 3.The apparatus defined in claim 1 comprising means forming a guidingconnection between said main frame and said upper portion of saidsupplemental frame providing for limited movement of said supplementalframe with respect to said frame top.
 4. The apparatus defined in claim2 comprising means forming a guiding connection between said main frameand said upper portion of said supplemental frame providing for movementof said supplemental frame with respect to said main frame within thelimits established by said resilient means to isolate said supplementalframe from the effects of relative movement of said base and top.
 5. Theapparatus defined in claim 1 wherein said upper and lower portions ofsaid supplemental frame are interconnected by a mid-portion definingtherewith a substantially C-shaped yoke with said upper and lowerportions extending substantially normal to the direction of movement ofsaid upper wheel on said frame top.
 6. The apparatus defined in claim 5wherein said mounting means (f) Comprises
 7. The apparatus defined inclaim 1 wherein said upper and lower portions of said supplemental frameare interconnected at both ends thereof by end portions cooperatingtherewith to enclose said opening for receiving the web therethrough.